In some cases--e.g. for vehicles or for emergency supply sources--the positive electrodes of lead-acid storage batteries are so called tubular plates, also known as tube type battery plates. In this case, the active material, surrounding the conducting lead rod, is covered with acid-resisting textile material so that the active material will not fall down from the conductor. The tubular plates are conventionally made by pulling the current collecting rods, which are connected to the current distributing bridge into the tube sheath, made from textile, and the dry mixture, composed of oxidized lead-powder and auxiliaries, is filled into the space between the rod and the sheath with vibration. This process is very dangerous because of the dusting of the lead-oxide powder and there isn't any perfect protection in spite of the great costs. In order to eliminate this problem, the so called wet filling method was developed. The known procedures are concerned first of all with the new results of developing the filling apparatus as described in the German Pat. No. 2 936 025 or U.S. Pat. No. 3,228,796. In the U.S. Pat. No. 4,037,630 the application of wet active material and a filling apparatus is described. The active material is a mixture of water and lead-oxide and its homogeneity is ensured by permanent mixing. This method has the disadvantage that the lead-oxide powder settles down in the water because of its 9 g/cc density, so this active material isn't practically homogeneous; it doesn't keep its consistence. In British Pat. No. 1 488 953 a complicated and expensive apparatus solves the problem of the processability of unstable material with continuous circulation and special stream system. The other disadvantage of the unstable consistence is that the part of the mixture that is rich in water will escape through the porous wall of the textile sheets; therefore this textile material must meet very strict requirements.
In British Pat. No. 1 475 490 the discharge of this mixture through the pores of the textile tubes is prevented by mixing sulfuric acid, water and sulfuric acid-resiting fibrous material to the active material in addition to lead oxides. The active material is extruded into the porous textile tubes under pressure and then due to the pressure, the liquid part of the pulp, moving through the pores of tubes, will carry the particles of the fibrous material to the internal wall of the tube.
In this way the coating on the internal wall of the tubes formed from the fibrous material will operate as a filter and lets only the liquid-phase of the active material flowing out through the wall of the textile tubes.
This method has the disadvantage that the structure of the active material will be non-homogeneous along the cross-section of the tubes because of the decrease of the fibrous material along the axis of the tubes.
In order to eliminate the dangereous dusting during the filling process--as described in the U.S. Pat. No. 4,252,872--two percent of polytetrafluorethylene (PTFE) is added to the oxidized lead powder either as a dry powder or in suspension. Then the mixture is heated. Thereby the PTFE changes from a powder to fibres. This fibrous PTFE will convert the 1-20 .mu.m particles of the lead oxide powder into granules having the dimensions 100-250 .mu.m, so the dusting will decrease.
The application of PTFE is described in the U.S. Pat. No. 4,110,519, first of all for the production of lubricated electrodes for storage batteries. In this case the active material is set into the windows of the conducting grid by lubrication and the finished electrode isn't covered with a textile-like material. By this type of electrode the connection between the active material and the conductor is very important; if the bond between them isn't strong enough, the active material will fall out of the grid during the operation. According to this patent an adhesive and coherent active material is available by mixing 0.1 to 3% weight percent PTFE with dry lead-oxide powder at the temperature of 80.degree. C. and possibly with MgSO.sub.4 inaddition. After mixing the dry powder, water or water and sulfuric acid is added and the mixing goes on. The stability of the mixture--that is the period while the active material keeps the viscosity adjusted in the mixer--isn't described. According to our observations, this type of active material has to be processed in a few hours and some laintance could happen even in this case.
Some decades ago glycerine was used for the production of lubricated electrodes to get a cement-like hardening active material. This application is described--among others--in the book C. Drucker and Dr. A. Finkelstein: Galvanische Elemente and Akkumulatoren (Akademisohe Verlag GmbH, Lepzig, 1932).
Nowadays glycerine isn't used, probably because of water evolution during the formation of the lead-glycerate. This water, formed during the drying after the lubrication, increases the inclination of the active material to crack and, so decreases the lifetime of the lubricated electrode.